Infected CCleaner downloads from official servers

In a supply chain attack that may be unprecedented in the number of downloads, servers hosting CCleaner, a popular tool for cleaning up the PC, has been delivering a version of the said software with malware.

What happened?

Threat actors have managed to change the files that were being delivered by Avast servers hosting CCleaner updates. In case you are wondering why they were on those servers, Avast acquired Piriform, the original publishers of CCleaner, a few months ago.

The incident was discovered and reported by Talos. Piriform is aware of the situation and is acting to prevent further damage. They are also investigating how the files coming from their servers were modified before being released to the public.

Possible impact

It is difficult to say at this moment how many users might have been affected, but the numbers could be huge. From the statistics brought out by Piriform, CCleaner has been downloaded 2 billion times in total, 5 million times every week. The modified version, 5.33, is made available from August 15 until September 12 when version 5.34 was released. In a press statement the company estimates that 2.27 million people used the affected software.

The malware

The malware collects the following information about the infected system:

What to do if you think you are affected?

First of all, check the version of CCleaner on your system. If you suspect you may have downloaded CCleaner version 5.33.6162 or CCleaner Cloud version 1.07.3191, scan your system for malware.

CCleaner users that are running older versions or that do not trust the one they are using now are encouraged to update their CCleaner software to version 5.34 or higher. The latest version is available for download here.

Affected versions: CCleaner version 5.33.6162 and CCleaner Cloud version 1.07.3191

Malwarebytes blocks the IP and domains related to this malware. We also remove the malicious installer.

In addition, Lunarsoft has reported in the past about why CCleaner’s usage on Windows has become obsolete in this day and age. With this recent malware infection being spread to millions of users, it’s another sign that it’s good to ditch CCleaner. With how Avast acquired Piriform, maybe the anti-virus company can help save it and improve the product. Time will tell.